The objective of the proposed research is to develop a procedure that can be used to characterize groundwater contamination at hazardous waste sites. We are particularly concerned with the design of characterization tools which can adapt to complex environmental conditions. The project will be an extension of new site characterization methods developed by the principal investigator and his coworkers (Graham and McLaughlin 1989a,b; Graham and McLaughlin, in press; Li and McLaughlin, in press). These methods produce realistic multi-dimensional maps of subsurface contaminant concentration by combining field measurements with mathematical models. The project proposed here will expand previous work to include important sources of uncertainty that have been ignored in the past. These additional sources include spatial and temporal variability in groundwater recharge, spatial variability in sorption and biodegradation properties, and uncertainties in the location and size of contaminant sources. We plan to test our extended site characterization procedure at a hazardous waste site in the Aberjona River Basin. The data needed to develop a statistical description of natural variability at the site will be collected as part of a team effort which will involve participation by Profs. Gschwend, Krumholz, Gelhar, and Hemond. The ultimate product of our site characterization procedure will be an efficient system for describing subsurface contamination both before and during remediation. The computer algorithms used in this procedure will be available to interested parties and the basic concepts will be summarized in articles published in the refereed literature.